Hydroformed tubes are attractive for automotive vehicles because they provide part consolidation and stiff structures. Hydroformed tubes are formed by placing the desired bends in the tube and forming the tube to the desired configuration. The process usually requires placing a tubular member having an open bore in a mold and sealing the ends of the tube. A pressurized liquid is then injected into the open bore, causing the tube to stretch and expand out against the mold.
In space-frame vehicle architecture, one hydroformed tube may need to be joined to another hydroformed tube. One joining method used to join one tube to another is welding one tube surface to another tube surface. However, the closed nature of hydroformed tubes imposes practical constraints when using conventional welding techniques, such as gas metal arc welding. Resistance welding is another type of welding that may be employed; however, when there are large contact surfaces (as there is with the hydroformed tubes), a very large current is required to generate enough heat to form a weld through resistance welding. In turn, the large current mandates a large transformer. Thus, resistance welding becomes an impractical method of welding hydroformed tubes.